That is a difficult situation to be in, but know that you are in good company and that it happens to the best of us. To me it usually happens when I talk to one of my bosses, and sadly (unintentionally) it usually affects my co-workers rather than myself, which in turn to them they think I am two-faced of sly sometimes. I am really not (or try not to be), but sometimes the nervousness gets the best of me and I divulge more than I should or stammer out comments I probably shouldn't be making.

Please try not to beat yourself up too hard over it and just take it as another stepping stone. I read a quote one time saying something along the lines that some of us donts make the same mistake once, we make it hundreds of times to make sure of how not to do something. I think this applies nicely here in that one day soon we'll be able to overcome the nervousness and pressure to not trip up on what others like to call "simple stuff".